Powered impact tool

ABSTRACT

A powered impact tool, such as an automatic hammer, chisel, star drill, or the like, is provided which comprises a spring loaded anvil mounted at one end of a housing; a spring loaded plunger, or piston, mounted within the housing; a carriage which slides reciprocally within the housing; a drive for the carriage which imparts the desired reciprocal movement to the carriage; and a pawl which releasably couples the piston to the carriage to permit the carriage to draw the piston back against its spring, and which releases the piston at a selected point of each stroke of the carriage so that the piston spring drives the piston against the anvil which in turn drives the anvil through the end of the housing so that the anvil may provide a high impacting force on the nail or other object being impacted by the tool. An adjustable trigger is also provided by which the displacement of each stroke of the piston, and thus the impact with which it strikes the anvil, can be controlled.

United States Patent 1191 Mitchell POWERED IMPACT TOOL Inventor: William C. Mitchell, 23152 Bigler St., Woodland Hills, Calif. 91364 Filed: May 15, 1972 Appl. No.: 253,434

[56] References Cited UNITED STATES PATENTS 5/1965 Sussmann 173/119 X 4/1968 Willis 1 .1 173/115 X 1,901,981 3/1933 Ousback 173/117 X 3,135,340 6/1964 Robinsky 173/115 FOREIGN PATENTS OR APPLICATIONS 810,498 7/1949 Germany 173/119 636,889 1/1928 France ..173/119 Primary ExaminerErnest Purser Assistant ExaminerWilliam F. Pate III Attorney, Agent, or Firm-Keith D. Beecher 1451 Jan. 29, 1974 5 7] ABSTRACT A powered impact tool, such as an automatic hammer, chisel, star drill, or the like, is provided which comprises a spring loaded anvil mounted at one end of a housing; a spring loaded plunger, or piston, mounted within the housing; a carriage which slides reciprocally within the housing; a drive for the carriage which imparts the desired reciprocal movement to the carriage; and a pawl which releasably couples the piston to the carriage to permit the carriage to draw the piston back against its spring, and'which releases the piston at a selected point of each stroke of the carriage so that the piston spring drives the piston against the anvil which in turn drives the anvil through the end of the housing so that the anvil may provide a high impacting force on the nail or other object being impacted by the tool. An adjustable trigger is also provided by which the displacement of each stroke of the piston, and thus the impact with which it strikes the anvil, can be controlled.

7 Claims, 5 Drawing Figures A -zz- 5 1 POWERED IMPACT TOOL BACKGROUND OF THE INVENTION Power tools are known in which a reciprocating striking plunger, or piston, acts upon a head, or anvil, so that the anvil may produce an impacting force. The anvil may itself constitute the impacting tool, as in the case of a powered hammer, or it may serve to receive the tool, such as a chisel, star drill, or the like.

In U.S. Pat. No. 1,310,574, for example, an automatic spring-actuated hammer is described in which a spring is periodically put under tension by means of an electric motor, and periodically released in order to impart to the hammer an impact pressure corresponding to the force stored up in the spring by its previous tensioning.

The impact tool of the present invention represents an improved mechanism which is similar in some-respects to the mechanism described in the aforesaid patent, and one in which a head or anvil is struck repeatedly by a spring loaded plunger or piston which is periodically drawn back against a resilient pressure and released, so that sufficient impact force may be developed at the head to drive nails, or the like, without the concomitant need for an excessively large mechanism.

The impact tool to be described is also advantageous in that the stroke displacement of the piston, and the resulting impact pressure of the head, can be controlled by the operator. In this way, at the beginning of an operation, the head may be driven at a relatively low impact, so as to start the nail, for example. Then the tool can be controlled so that the head is driven at an increased impact to drive the nail home. When the tool is usedto drive a star drill or chisel, as for example, in the sculpting of stone or wood, the magnitude of impact is readily controllabe to suit the particular applicatron.

BRIEF DESCRIPTION OF THE DRAWINGS tially along the line 4-4 of FIG. I; and

FIG. 5 is a further section taken along the line 55 of FIG. 1.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT A tool shown in FIG. 1 includes, for example, a housing 10. A pistol grip 12 is attached to the housing. A forward grip 14 is attached to the forward end a of the housing, the grip having a generally tubular configuration. In the operation of the tool, it is grasped by the pistol grip l2, and by the forward grip l4, and is operated by pressing a trigger 16 in the pistol grip 12.

An electric motor 20 is attached to the rear end of the housing 10, and the motor is powered through an electric cable 22. If desired, the electric motor may be replaced by an air operated motor, or other power source. An anvil 26 protrudes from the forward end of the tubular portion 10a of housing 10, and this latter member forms a head for the tool. The heat itself may be used as an impactor, when the tool is used as a powered hammer.'Alternatively, the head may be configured to receive an appropriate tool, such as suggested above.

As shown in FIG. 2, the anvil 26 is resiliently biased inwardly into the tubular member by a coil spring 32. A thin sleeve 30 is used to limit the travel of the anvil 26 to the left. A piston 34 is slidably mounted in the tubular portion 10a .in coaxial relationship with the anvil 26, and a coil spring 36 resiliently biases the piston 34 to the right in FIG. 2 into an impact relationship with the anvil 26, causing the anvil likewise to be moved to the right in FIG. 2. Then when the piston 34 is moved back to the left, in FIG. 2, the anvil'26 again assumes its illustrated position, under the biasing pressure of-its spring 32. It will be appreciated that the spring 32 is a relatively weak spring, and its only function is to return the anvil 26 to its retracted position, when the piston 34 is withdrawn. The spring 36, on the other hand, is a strong spring, so that when the piston 34 is released, the spring 36 drives it with high impact against the anvil 26.

As shown in FIG. 3, a carriage 40 is slidably mounted in the housing 10 for reciprocal movement in the housing along the common axis of the piston 34 and anvil 26. The carriage 40 is reciprocally moved along the axis within the housing 10 by means of a drive gear 42 which is coupled to the carriage by means of an eccentric drive pin 44. The pin 44 is mounted, on the drive gear 42, and engages a transverse slot in the upper surface of the carriage 40. Then, as the drive gear 42 rotates, the carriage 40 moves reciprocally back and forth within the housing If).

FIG. 4 illustrates one possible configuration of drive gearing for the tool. The drive gear 42 is driven, for example, by the electric motor 20'through a pinion 50 which is mounted on the drive shaft 52 of the motor. The pinion 50 is coupled to a gear 54, which is mounted coaxially with a'pinion 56. The pinion 56, in turn, is coupled through a gear 58 to a further gear 60. The gear 60, in turn, is connected to a worm gear 62, the worm gear 62 being coupled to the drive gear 42 of- FIG. 3, so that the gear 42 rotates, to impart the desired reciprocating motion to the sliding carriage 40, when the electric motor 20 is energized.

A pawl 64 is pivotally mounted on the carriage 40 by means of a pin 66, and a spring 68 biases the pawl into engagement with the end of a connecting rod 70. The connecting rod 70 is connected to the piston 34, and extends coaxially into the housing 10, as shown in FIG. 3. The pawl 64 normally engages the end of the connecting rod 70, so that when the carriage 40 moves to the left in FIG. 3, it draws the piston 34 with it against the pressure of the spring 36. However, at a particular point in the travel of the sliding carriage to the left in FIG. 3, the end of the pawl 64 engages a cam 72, and this releases the pawl 64 permitting the piston 34 to move rapidly to the right in FIG. 3 under the action of the spring 36. During the next cycle, the pawl 64 again engages the connecting rod 70, and the operation is repeated. The cam 72 is supported on a rod 74 which is spring loaded by a cam spring 76.

As best shown in FIG. 5, the trigger 16 in the pistol grip 12 is coupled to a lever 78. The lever 78 is pivotally mounted at the end of the handle by a pin 80, and

its other end extends into a slot in the cam 72. The lever serves as a cam positioning control, so that operation of the trigger 16 by moving it to the left in FIG. 5, causes the cam 72 to move against the tension of its spring 76. This results in a positioning of the cam 72 which, in turn, determines the point at which the pawl 64 is released.

For example, when the cam 72 is positioned to its extreme right-hand position, as illustrated in FIG. 3, the

pawl is released early in the stroke of the carriage, and this results in relatively short movements of the piston 34, and resulting relatively low impacts of the piston against the anvil 26. Then, when the trigger 16 is depressed, the lever 78 moves the cam to the right in FIG. 3, resulting in longer strokes of the piston 34, and higher impacts against the anvil 26. This control, as mentioned above, is convenient since at the start, for example, of a nailing operation, the nail may be started by a series oflow impacts by the head of the tool. Then, as the nail is driven into place, the trigger may be moved further into the pistol grip, resulting in higher impacts to drive the nail into its final position. Also, when the tool is used for other hammering, chiseling or drilling operations, it may be controlled to provide the magnitude of impacts suitable to the particular application.

An electric switch 90 is mounted within the pistol grip 12, as shown in FIG. 5, on a leaf spring 92. In this way, when the trigger 16 is first moved into the pistol grip, it closes the switch to activate the electric motor 20. Further movement of the trigger into the pistol grip causes the switch to move with it against the resilience of the leaf spring 92.

The invention provides, therefore, an improved impacting tool, which is relatively simple in its construction, and is of relatively small size. The tool of the invention, as described, provides for high impact operation of its head, with a relatively small sized instrument. Also, the impact pressure exerted by the head is readily controllable by the tool, as described above.

While a particular embodiment of the invention has been described, modifications may be made. For example, a dual pawl, symmetrical variation of the illustrated embodiment may be utilized. It is intended, therefore, in the following claims to cover all modifications which come within the. spirit and scope of the invention.

What is claimed is:

1. An automatic power impact tool comprising: an

elongated housing; handle means for holding the housing stationary while the tool is in operation; an anvil slidably mounted at one end of the stationary housing and projecting therefrom to form a head for the tool; a first resilient means coupledto said stationary housing and to said anvil for biasing said anvil inwardly with respect to said housing; a piston slidably mounted in said housing independently of said anvil in axial alignment with said anvil; a second resilient means coupled to said housing and to said piston for driving said piston along said housing towards said anvil to cause said piston to impact with said anvil and drive said anvil outwardly with respect to said housing and against the biasing action of said first resilient means; a carriage slidably mounted in said housing at the opposite end thereof to said anvil and in spaced axial alignment with respect to said piston; a drive means coupled to said carriage for imparting reciprocal movement to said carriage within said housing coaxially with said piston; pawl means releasably coupling said piston to said carriage to cause said piston to be moved by said carriage against the action of said second resilient means; and cam means mounted in said housing in position to engage said pawl means at a particular point of each stroke of said carriage to release said piston.

2. The combination defined in claim 1, in which said drive means comprises an electric motor and transmission gear means coupling said motor to said carriage.

3. The combination defined in claim 1, in which said first and second resilient means comprise respectively first and second coil springs.

' 4. An automatic power impact tool comprising: a housing; an anvil slidably mounted at one end of the housing and projecting therefrom to form a head for the tool; a first resilient means coupled to said housing and to said anvil for biasing said anvil inwardly with respect to said housing; a piston slidably mounted in said housing in axial alignment with said anvil; a second resilient means coupled to said housing and to said piston for driving said piston towards said anvil to cause said piston to impact with said anvil and drive said anvil outwardly with respect to said housing and against the biasing action of said first resilient means; a carriage slidably mounted in said housing; a drive means coupled to said carriage for imparting reciprocal movement to said carriage; pawl means releasably coupling said piston to said carriage to cause said piston to be moved by said carriage against the action of said second resilient means; cam means mounted in said housing in position to engage said pawl means at a particular point of each stroke of said carriage to release said piston; and manually operated control means coupled to said cam means to adjust the position of said point at which said piston is released.

S. The combination defined in claim 4, and which includes a pistol grip affixed to said housing, and in which said manually operated control means comprises a trigger member mounted in said pistol grip.

6. The combination defined in claim 2, in which said transmission gear means includes a drive gear and an eccentric drive pin engaging a slot in said carriage for converting rotary. motion into reciprocating motion, and a worm gear for imparting speed reduction between the electric-mot'or and the carriage.

7. The combination defined in claim 6, in which said electric motor includes a drive shaft axially aligned with the axis of said piston, and gear means coupling said drive shaft to said worm gear. l =l= i 

1. An automatic power impact tool comprising: an elongated housing; handle means for holding the housing stationary while the tool is in operation; an anvil slidably mounted at one end of the stationary housing and projecting therefrom to form a head for the tool; a first resilient means coupled to said stationary housing and to said anvil for biasing said anvil inwardly with respect to said housing; a piston slidably mounted in said housing independently of said anvil in axial alignment with said anvil; a second resilient means coupled to said housing and to said piston for driving said piston along said housing towards said anvil to cause said piston to impact with said anvil and drive said anvil outwardly with respect to said housing and against the biasing action of said first resilient means; a carriage slidably mounted in said housing at the opposite end thereof to said anvil and in spaced axial alignment with respect to said piston; a drive means coupled to said carriage for imparting reciprocal movement to said carriage within said housing coaxially with said piston; pawl means releasably coupling said piston to said carriage to cause said piston to be moved by said carriage against the action of said second resilient means; and cam means mounted in said housing in position to engage said pawl means at a particular point of each sTroke of said carriage to release said piston.
 2. The combination defined in claim 1, in which said drive means comprises an electric motor and transmission gear means coupling said motor to said carriage.
 3. The combination defined in claim 1, in which said first and second resilient means comprise respectively first and second coil springs.
 4. An automatic power impact tool comprising: a housing; an anvil slidably mounted at one end of the housing and projecting therefrom to form a head for the tool; a first resilient means coupled to said housing and to said anvil for biasing said anvil inwardly with respect to said housing; a piston slidably mounted in said housing in axial alignment with said anvil; a second resilient means coupled to said housing and to said piston for driving said piston towards said anvil to cause said piston to impact with said anvil and drive said anvil outwardly with respect to said housing and against the biasing action of said first resilient means; a carriage slidably mounted in said housing; a drive means coupled to said carriage for imparting reciprocal movement to said carriage; pawl means releasably coupling said piston to said carriage to cause said piston to be moved by said carriage against the action of said second resilient means; cam means mounted in said housing in position to engage said pawl means at a particular point of each stroke of said carriage to release said piston; and manually operated control means coupled to said cam means to adjust the position of said point at which said piston is released.
 5. The combination defined in claim 4, and which includes a pistol grip affixed to said housing, and in which said manually operated control means comprises a trigger member mounted in said pistol grip.
 6. The combination defined in claim 2, in which said transmission gear means includes a drive gear and an eccentric drive pin engaging a slot in said carriage for converting rotary motion into reciprocating motion, and a worm gear for imparting speed reduction between the electric motor and the carriage.
 7. The combination defined in claim 6, in which said electric motor includes a drive shaft axially aligned with the axis of said piston, and gear means coupling said drive shaft to said worm gear. 